The present invention relates to bending springs made of fiber compound materials in which fiber threads or strands are embedded in a resinous impregnating material which is bonded to the fibers which extend unidirectionally throughout the length of the bending spring. The invention relates especially to bent leaf springs.
Springs of this type are disclosed, for example, in U.S. Pat. No. 3,142,598. Such springs are frequently constructed in such a manner that the individual bent spring leaf is made of unidirectionally oriented glass fiber strands which extend over the entire length of the leaf spring and which are resin impregnated or embedded in a resinous bonding matrix. In other words, the cured or hardened resin functions as a matrix and as a bonding agent for the fibers. Thus, the resinous matrix must necessarily also take up the forces which result due to the bending load or stress applied to the fiber strands. Such loading may become critical where the bending load results in a bending of the spring in a direction contrary to the original bend of the spring. Such critical loading is due to the fact that the resinous matrix must secure the fiber strands against fanning out or a separation of the strands from the resinous matrix under the then effective transverse stress. Such transverse stress results from the radial components of the forces extending normally due to the torque load applied to the spring. The bonding action of the resinous matrix, or rather, between the resinous matrix and the fiber strands against these transverse stresses, must be satisfied by the resinous matrix, the more so the larger the thickness of the spring and the larger the original bend of the spring is. Therefore, high strength requirements must be satisfied by the resinous matrix. Heretofore, prior art structures of this type have not always satisfied these requirements.